Defibrillation waveforms for a wearable cardiac defibrillator

ABSTRACT

An external defibrillator system is configured with at least two different algorithms for determining the duration of a shock administered to a patient being treated and selects the algorithm based on one or more patient parameters such as, for example, the patient&#39;s TTI. The patient&#39;s TTI can be measured prior to or while the shock is being administered to the patient. The shock can be, for example, a multiphasic defibrillation or a multiphasic cardioversion shock. The charge voltage of the system&#39;s energy storage device can additionally be varied depending on the one or more patient parameters. For example, the system may charge the energy storage device so that the charge voltage is higher or lower than a nominal charge voltage responsive to the patient&#39;s TTI is higher or lower compared to an average TTI, respectively.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

The present patent application is a continuation of U.S. applicationSer. No. 15/794,585 filed Oct. 26, 2017, which in turn claims benefit ofU.S. Application No. 62/512,003 filed May 27, 2017 and the benefit ofU.S. Application No. 62/550,518 filed Aug. 25, 2017, all of which arehereby incorporated by reference in their entireties.

BACKGROUND

When people suffer from some types of heart arrhythmias, the result maybe that blood flow to various parts of the body is reduced. Somearrhythmias may even result in a Sudden Cardiac Arrest (SCA). SCA canlead to death very quickly, e.g. within 10 minutes, unless treated inthe interim.

Some people have an increased risk of SCA. People at a higher riskinclude patients who have had a heart attack, or a prior SCA episode. Afrequent recommendation is for these people to receive an ImplantableCardioverter Defibrillator (ICD). The ICD is surgically implanted in thechest, and continuously monitors the patient's electrocardiogram (ECG).If certain types of heart arrhythmias are detected, then the ICDdelivers an electric shock through the heart.

After being identified as having an increased risk of an SCA, and beforereceiving an ICD, these people are sometimes given a WearableCardioverter Defibrillator (WCD) system (early versions of such systemswere called wearable cardiac defibrillator systems). A WCD systemtypically includes a harness, vest, or other garment that the patient isto wear. The WCD system further includes electronic components, such asa defibrillator and electrodes, coupled to the harness, vest, or othergarment. When the patient wears the WCD system, the external electrodesmay then make electrical contact with the patient's skin, and thereforecan help determine the patient's ECG. If a shockable heart arrhythmia isdetected, then the WCD system may deliver the appropriate electric shockthrough the patient's body to try to defibrillate or cardiovert thepatient's heart.

SUMMARY

In embodiments, a system includes an external defibrillator configuredwith at least two different algorithms for determining the duration of ashock administered to a patient being treated. In some embodiments, thedefibrillator is configured with at least three different algorithms fordetermining the duration of the shock. In some embodiments, the systemcan include a WCD.

In some embodiments, a method of delivering a shock is configured toselect from at least two different algorithms for determining theduration of the shock. In some embodiments, the method selects from atleast three different algorithms for determining the duration of theshock.

In some embodiments, the at least two algorithms for determining theduration can be based on the Walcott algorithm and the Constant Energyalgorithm (“CE algorithm”). In some embodiments, the at least twoduration algorithms include a third duration algorithm such as, forexample, an algorithm that sets the duration to preconfigured maximumduration without regard to the patient's TTI or durations of thewaveform's periods or phases (referred to herein as a “Max Durationalgorithm”). In some embodiments, the maximum duration is less than orequal to 25 ms. In some embodiments, other shock duration algorithms canbe used in place of or in addition to the Max Duration, Walcott and CEalgorithms, including modified versions of the Max Duration, Walcott andCE algorithms.

In some embodiments, the shock can be, for example, a defibrillationshock or a cardioversion shock. In some embodiments, the shock can be amultiphasic shock such as, for example, a biphasic truncated exponentialshock. In some embodiments, the system or method is configured to selectthe duration algorithm based on one or more patient parameters such as,for example, the patient's transthoracic impedance (TTI) or a time foran energy storage module to discharge to a selected or set ratio. Insome embodiments, the one or more patient parameter is measured beforethe shock is administered, and in some other embodiments while the shockis being administered to the patient.

In some embodiments, an energy storage device such as, for example, acapacitor is used to provide the energy for the shock that isadministered to the patient. In some embodiments, in addition to usingtwo or more algorithms to determine the duration of the shock, thecharge voltage of the energy storage device can be varied depending onthe patient's TTI. For example, in some embodiments the system maycharge the energy storage device so that the charge voltage is higher orlower than a nominal charge voltage responsive to the patient's TTIbeing higher or lower compared to a predetermined average TTI,respectively.

The foregoing brief summary is illustrative only and is not intended tobe in any way limiting. In addition to the illustrative aspects,embodiments, and features described above, which need not all be presentin all embodiments of the inventions disclosed herein, further aspects,embodiments, and features are set forth in the drawings and thefollowing detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of components of a sample wearable cardioverterdefibrillator (WCD) system, made according to embodiments.

FIG. 2 is a diagram showing sample components of an externaldefibrillator, such as the one illustrated in the system of FIG. 1 , andwhich is made according to embodiments.

FIG. 3 is a diagram showing sample components of an externaldefibrillator similar to the external defibrillator of FIG. 2 , in whichsome components are shown in more detail, according to embodiments.

FIGS. 4A-4B are diagrams showing energy delivery of an example biphasictruncated exponential (BTE) waveform, according to embodiments.

FIG. 5 is a flow diagram showing methods for determining shock duration,according to embodiments.

FIG. 6 is a flow diagram showing additional methods for determiningshock duration, according to embodiments.

FIG. 7 is a flow diagram showing methods for determining charge voltageand shock duration, according to embodiments.

FIG. 8 is a diagram showing sample components of an externaldefibrillator similar to the external defibrillator of FIGS. 2 and 3 ,in which some components are shown in more detail, according toembodiments.

FIG. 9 is a flow diagram showing additional methods for determiningshock duration and selecting a shock waveform, according to embodiments.

DETAILED DESCRIPTION

A wearable cardioverter defibrillator (WCD) system made according toembodiments has several components. These components can be providedseparately as modules that can be interconnected, or can be combinedwith other components, etc.

FIG. 1 depicts a patient 82. Patient 82 may also be referred to as aperson and/or wearer, since that patient wears components of the WCDsystem.

FIG. 1 also depicts components of a WCD system made according toembodiments. One such component is a support structure 170 that iswearable by patient 82. It will be understood that support structure 170is shown generically in FIG. 1 , and partly conceptually. FIG. 1 isprovided to illustrate concepts about support structure 170, and is notto be construed as limiting how support structure 170 is implemented, orhow it is worn.

Support structure 170 can be implemented in many different ways indifferent embodiments. For example, in one embodiment support structure170 is be implemented in a single component or a combination of multiplecomponents. In some embodiments, support structure 170 includes a vest,or a half-vest, or shirt, or other type garment, etc. In suchembodiments, such items can be worn similarly to parallel articles ofclothing. In some embodiments, support structure 170 include a harness,one or more belts or straps, etc. In such embodiments, such items can beworn by the patient around the torso, hips, over the shoulder, etc. Insome embodiments, support structure 170 includes a container or housing,which in some embodiments is waterproof. In such embodiments, thesupport structure can be worn by being attached to the patient byadhesive material, for example as shown in U.S. Pat. No. 8,024,037. Insome embodiments, support structure 170 is implemented as described forthe support structure of US Pat. App. No. US 2017/0056682A1, which isincorporated herein by reference. Of course, in such embodiments, inview of this disclosure a person skilled in the art will recognize thatadditional components of the WCD system can be in the housing of asupport structure instead of attached externally to the supportstructure, for example as described in the document incorporated byreference. There can be other examples.

A WCD system according to embodiments is configured to defibrillate apatient who is wearing it, by delivering an electrical charge to thepatient's body in the form of an electric shock delivered in one or morepulses. FIG. 1 shows a sample external defibrillator 100, and sampledefibrillation electrodes 104, 108, which are coupled to externaldefibrillator 100 via electrode leads 105. Defibrillator 100 anddefibrillation electrodes 104, 108 are coupled to support structure 170.As such, many of the components of defibrillator 100 can be thereforecoupled to support structure 170. When defibrillation electrodes 104,108 make good electrical contact with the body of patient 82,defibrillator 100 can administer, via electrodes 104, 108, a brief,strong electric pulse 111 through the body. Pulse 111, also referred toherein as a shock, a defibrillation shock, a cardioversion shock,therapy or therapy shock, is intended to go through and restart heart85, in an effort to save the life of patient 82. In some embodimentspulse 111 includes one or more pacing pulses, and so on.

A prior art defibrillator typically decides whether to defibrillate ornot based on an ECG signal of the patient. However, externaldefibrillator 100 may initiate a shock (or hold-off a shock) based on avariety of inputs, with ECG merely being one of them.

Accordingly, in some embodiments of defibrillator 100, signals such asphysiological signals containing physiological data are obtained frompatient 82. While the patient may be a considered also a “user” of theWCD system, in some embodiments, for example, a user of the wearablecardioverter defibrillator (WCD) may be a clinician such as a doctor,nurse, emergency medical technician (EMT) or other similarly situatedindividual (or group of individuals). The particular context of theseand other related terms within this description should be interpretedaccordingly.

The WCD system may optionally include an outside monitoring device 180.Device 180 is called an “outside” device because it could be provided asa standalone device, for example not within the housing of defibrillator100. Device 180 can be configured to sense or monitor at least one localparameter. A local parameter can be a parameter of patient 82, or aparameter of the WCD system, or a parameter of the environment, as willbe described later in this document. Device 180 may include one or moretransducers or sensors that are configured to render one or morephysiological inputs from one or more patient parameters that it senses.

Optionally, device 180 is physically coupled to support structure 170.In addition, device 180 can be communicatively coupled with othercomponents, which are coupled to support structure 170. Suchcommunication can be implemented by a communication module, as will bedeemed applicable by a person skilled in the art in view of thisdescription.

FIG. 2 is a diagram showing components of an external defibrillator 200,made according to embodiments. These components can be, for example,included in external defibrillator 100 of FIG. 1 . The components shownin FIG. 2 can be provided in a housing 201, which may also be referredto as casing 201.

External defibrillator 200 is intended for a patient who would bewearing it, such as patient 82 of FIG. 1 . Defibrillator 200 may furtherinclude a user interface 280 for a user 282. User 282 can be patient 82,also known as wearer 82. Or user 282 can be a local rescuer at thescene, such as a bystander who might offer assistance, or a trainedperson. Or, user 282 might be a remotely located trained caregiver incommunication with the WCD system.

User interface 280 can be made in many ways. User interface 280 mayinclude output devices, which can be visual, audible or tactile, forcommunicating to a user by outputting images, sounds or vibrations.Images, sounds, vibrations, and anything that can be perceived by user282 can also be called human perceptible indications. There are manyexamples of output devices. For example, an output device can be alight, or a screen to display what is sensed, detected and/or measured,and provide visual feedback to rescuer 282 for their resuscitationattempts, and so on. Another output device can be a speaker, which canbe configured to issue voice prompts, beeps, loud alarm sounds to warnbystanders, etc.

User interface 280 may further include input devices for receivinginputs from users. Such input devices may additionally include variouscontrols, such as pushbuttons, keyboards, touchscreens, one or moremicrophones, and so on. An input device can be a cancel switch, which issometimes called an “I am alive” switch or “live man” switch. In someembodiments, actuating the cancel switch can prevent the impendingdelivery of a shock.

Defibrillator 200 may include an internal monitoring device 281. Device281 is called an “internal” device because it is incorporated withinhousing 201. Monitoring device 281 can sense or monitor patientparameters such as patient physiological parameters, system parametersand/or environmental parameters, all of which can be called patientdata. In other words, internal monitoring device 281 can becomplementary or an alternative to outside monitoring device 180 of FIG.1 . Allocating which of the system parameters are to be monitored bywhich monitoring device can be done according to design considerations.Device 281 may include one or more transducers or sensors (not shown)that are configured to render one or more physiological inputs from oneor more patient parameters that it senses.

Patient parameters may include patient physiological parameters. Patientphysiological parameters may include, for example and withoutlimitation, those physiological parameters that can be of any help indetecting by the wearable defibrillation system whether the patient isin need of a shock, plus optionally their medical history and/or eventhistory. Examples of such parameters include the patient's ECG, bloodoxygen level, blood flow, blood pressure, blood perfusion, pulsatilechange in light transmission or reflection properties of perfusedtissue, heart sounds, heart wall motion, breathing sounds and pulse.Accordingly, monitoring devices 180, 281 may include one or more sensorsconfigured to acquire patient physiological signals. Examples of suchsensors include electrodes to detect ECG data, a perfusion sensor, apulse oximeter, a Doppler device for detecting blood flow, a cuff fordetecting blood pressure, an optical sensor, illumination detectors andperhaps sources for detecting color change in tissue, a motion sensor, adevice that can detect heart wall movement, a sound sensor, a devicewith a microphone, an SpO₂ sensor, and so on. It will be appreciatedthat such sensors can help detect the patient's pulse, and can thereforealso be called pulse detection sensors, pulse sensors, and pulse ratesensors. Pulse detection is also taught at least in Physio-Control'sU.S. Pat. No. 8,135,462, which is hereby incorporated by reference inits entirety. In addition, a person skilled in the art may implementother ways of performing pulse detection. In such cases, the transducerincludes an appropriate sensor, and the physiological input is ameasurement by the sensor of that patient parameter. For example, theappropriate sensor for a heart sound may include a microphone, etc.

In some embodiments, the local parameter is a trend that can be detectedin a monitored physiological parameter of patient 282. A trend can bedetected by comparing values of parameters at different times.Parameters whose detected trends can particularly help a cardiacrehabilitation program include: a) cardiac function (e.g. ejectionfraction, stroke volume, cardiac output, etc.); b) heart ratevariability at rest or during exercise; c) heart rate profile duringexercise and measurement of activity vigor, such as from the profile ofan accelerometer signal and informed from adaptive rate pacemakertechnology; d) heart rate trending; e) perfusion, such as from SpO₂ orCO₂; f) respiratory function, respiratory rate, etc.; g) motion, levelof activity; and so on. Once a trend is detected, it can be storedand/or reported via a communication link, along perhaps with a warning.From the report, a physician monitoring the progress of patient 282 willknow about a condition that is either not improving or deteriorating.

Patient state parameters include recorded aspects of patient 282, suchas motion, posture, whether they have spoken recently plus maybe alsowhat they said, and so on, plus optionally the history of theseparameters. Or, one of these monitoring devices could include a locationsensor such as a Global Positioning System (GPS) location sensor. Such asensor can detect the location, plus a speed can be detected as a rateof change of location over time. Many motion detectors output a motionsignal that is indicative of the motion of the detector, and thus of thepatient's body. Patient state parameters can be very helpful innarrowing down the determination of whether SCA is indeed taking place.

A WCD system made according to embodiments may include a motiondetector. In embodiments, a motion detector can be implemented withinmonitoring device 180 or monitoring device 281. Such a motion detectorcan be configured to detect a motion event. In response, the motiondetector may render or generate from the detected motion event a motiondetection input that can be received by a subsequent device orfunctionality. A motion event can be defined as is convenient, forexample a change in motion from a baseline motion or rest, etc. Such amotion detector can be made in many ways as is known in the art, forexample by using an accelerometer. In such cases, the patient parameteris a motion, one of the transducers may include a motion detector, andthe physiological input is a motion measurement.

System parameters of a WCD system can include system identification,battery status, system date and time, reports of self-testing, recordsof data entered, records of episodes and intervention, and so on.

Environmental parameters can include ambient temperature and pressure.Moreover, a humidity sensor may provide information as to whether it islikely raining. Presumed patient location could also be considered anenvironmental parameter. The patient location could be presumed ifmonitoring device 180 or 281 includes a GPS location sensor as per theabove.

Defibrillator 200 typically includes a defibrillation port 210, such asa socket in housing 201. Defibrillation port 210 includes electricalnodes 214, 218. Leads of defibrillation electrodes 204, 208, such asleads 105 of FIG. 1 , can be plugged into defibrillation port 210, so asto make electrical contact with nodes 214, 218, respectively. It is alsopossible that defibrillation electrodes 204, 208 are connectedcontinuously to defibrillation port 210, instead. Either way,defibrillation port 210 can be used for guiding, via electrodes, to thewearer the electrical charge that has been stored in an energy storagemodule 250 that is described more fully later in this document. Theelectric charge will be the shock for defibrillation, pacing, and so on.

Defibrillator 200 may optionally also have an ECG port 219 in housing201, for plugging in sensing electrodes 209, which are also known as ECGelectrodes and ECG leads. It is also possible that sensing electrodes209 can be connected continuously to ECG port 219, instead. Sensingelectrodes 209 are types of transducers that can help sense an ECGsignal, e.g. a 12-lead signal, or a signal from a different number ofleads, especially if they make good electrical contact with the body ofthe patient. Sensing electrodes 209 can be attached to the inside ofsupport structure 170 for making good electrical contact with thepatient, similarly as defibrillation electrodes 204, 208.

Optionally a WCD system according to embodiments also includes a fluidthat it can deploy automatically between the electrodes and the patientskin. The fluid can be conductive, such as by including an electrolyte,for making a better electrical contact between the electrode and theskin. Electrically speaking, when the fluid is deployed, the electricalimpedance between the electrode and the skin is reduced. Mechanicallyspeaking, the fluid may be in the form of a low-viscosity gel, so thatit does not flow away, after it has been deployed. The fluid can be usedfor both defibrillation electrodes 204, 208, and sensing electrodes 209.

The fluid may be initially stored in a fluid reservoir, not shown inFIG. 2 , which can be coupled to the support structure. In addition, aWCD system according to embodiments further includes a fluid deployingmechanism 274. Fluid deploying mechanism 274 can be configured to causeat least some of the fluid to be released from the reservoir, and bedeployed near one or both of the patient locations, to which theelectrodes are configured to be attached to the patient. In someembodiments, fluid deploying mechanism 274 is activated prior to theelectrical discharge responsive to receiving activation signal AS fromprocessor 230 that is described more fully later in this document.

In some embodiments, defibrillator 200 also includes a transducer thatincludes a measurement circuit 220. Measurement circuit 220 senses oneor more electrical physiological signal of the patient from ECG port219, if provided. Even if defibrillator 200 lacks ECG port 219,measurement circuit 220 can obtain physiological signals through nodes214, 218 instead, when defibrillation electrodes 204, 208 are attachedto the patient. In these cases, the physiological input reflects an ECGmeasurement. The parameter can be an ECG, which can be sensed as avoltage difference between electrodes 204, 208. In addition, theparameter can be an impedance, which can be sensed between electrodes204, 208 and/or the connections of ECG port 219. Sensing the impedancecan be useful for detecting, among other things, whether theseelectrodes 204, 208 and/or sensing electrodes 209 are not making goodelectrical contact with the patient's body. These patient physiologicalsignals can be sensed, when available. Measurement circuit 220 can thenrender or generate information about them as physiological inputs, data,other signals, etc. More strictly speaking, the information rendered bymeasurement circuit 220 is output from it, but this information can becalled an input because it is received by a subsequent device orfunctionality as an input.

Defibrillator 200 also includes a processor 230. Processor 230 may beimplemented in many ways. Such ways include, by way of example and notof limitation, digital and/or analog processors such as microprocessorsand Digital Signal Processors (DSPs); controllers such asmicrocontrollers; software running in a machine; programmable circuitssuch as Field Programmable Gate Arrays (FPGAs), Field-ProgrammableAnalog Arrays (FPAAs), Programmable Logic Devices (PLDs), ApplicationSpecific Integrated Circuits (ASICs), any combination of one or more ofthese, and so on.

The processor 230 may include, or have access to, a non-transitorystorage medium, such as memory 238 that is described more fully later inthis document. Such a memory can have a non-volatile component forstorage of machine-readable and machine-executable instructions. A setof such instructions can also be called a program. The instructions,which may also be referred to as “software,” generally provide forfunctionality by performing methods as may be disclosed herein orunderstood by one skilled in the art in view of the disclosedembodiments. In some embodiments, and as a matter of convention usedherein, instances of the software may be referred to as a “module” andby other similar terms. Generally, a module includes a set of theinstructions so as to offer or fulfill a particular functionality.Embodiments of modules and the functionality delivered are not limitedby the embodiments described in this document.

Processor 230 can be considered to have a number of modules. One suchmodule can be a detection module 232. Detection module 232 can include aVentricular Fibrillation (VF) detector. The patient's sensed ECG frommeasurement circuit 220, which can be available as physiological inputs,data, or other signals, may be used by the VF detector to determinewhether the patient is experiencing VF. Detecting VF is useful, becauseVF results in SCA. Detection module 232 can also include a VentricularTachycardia (VT) detector, and so on.

Another such module in processor 230 can be an advice module 234, whichgenerates advice for what to do. The advice can be based on outputs ofdetection module 232. There can be many types of advice according toembodiments. In some embodiments, the advice is a shock/no shockdetermination that processor 230 can make, for example via advice module234. The shock/no shock determination can be made by executing a storedShock Advisory Algorithm. A Shock Advisory Algorithm can make a shock/noshock determination from one or more of ECG signals that are capturedaccording to embodiments, and determining whether a shock criterion ismet. The determination can be made from a rhythm analysis of thecaptured ECG signal or otherwise.

In some embodiments, when the determination is to shock, an electricalcharge is delivered to the patient. Delivering the electrical charge isalso known as discharging. Shocking can be for defibrillation, pacing,and so on.

Processor 230 can include additional modules, such as other module 236,for other functions. In addition, if internal monitoring device 281 isindeed provided, it may be operated in part by processor 230, etc.

Defibrillator 200 optionally further includes a memory 238, which canwork together with processor 230. Memory 238 may be implemented in manyways. Such ways include, by way of example and not of limitation,volatile memories, Nonvolatile Memories (NVM), Read-Only Memories (ROM),Random Access Memories (RAM), magnetic disk storage media, opticalstorage media, smart cards, flash memory devices, any combination ofthese, and so on. Memory 238 is thus a non-transitory storage medium.Memory 238, if provided, can include programs for processor 230, whichprocessor 230 may be able to read and execute. More particularly, theprograms can include sets of instructions in the form of code, whichprocessor 230 may be able to execute upon reading. Executing isperformed by physical manipulations of physical quantities, and mayresult in functions, operations, processes, actions and/or methods to beperformed, and/or the processor to cause other devices or components orblocks to perform such functions, operations, processes, actions and/ormethods. The programs can be operational for the inherent needs ofprocessor 230, and can also include protocols and ways that decisionscan be made by advice module 234. In addition, memory 238 can storeprompts for user 282, if this user is a local rescuer. Moreover, memory238 can store data. This data can include patient data, system data andenvironmental data, for example as learned by internal monitoring device281 and outside monitoring device 180. The data can be stored in memory238 before it is transmitted out of defibrillator 200, or stored thereafter it is received by defibrillator 200.

Defibrillator 200 may also include a power source 240. To enableportability of defibrillator 200, power source 240 typically includes abattery. Such a battery is typically implemented as a battery pack,which can be rechargeable or not. Sometimes a combination is used ofrechargeable and non-rechargeable battery packs. Other embodiments ofpower source 240 can include an AC power override, for where AC powerwill be available, an energy storage capacitor, and so on. In someembodiments, power source 240 is controlled by processor 230.Appropriate components may be included to provide for charging orreplacing power source 240.

Defibrillator 200 may additionally include an energy storage module 250.Energy storage module 250 can be coupled to the support structure of theWCD system, for example either directly or via the electrodes and theirleads. Module 250 is where some electrical energy can be storedtemporarily in the form of an electrical charge, when preparing it fordischarge to administer a shock. In embodiments, module 250 can becharged from power source 240 to the right amount of energy, ascontrolled by processor 230. In typical implementations, module 250includes a capacitor 252, which can be a single capacitor or a system ofcapacitors, and so on. In some embodiments, energy storage module 250includes a device that exhibits high power density, such as anultracapacitor. As described above, capacitor 252 can store the energyin the form of an electrical charge, for delivering to the patient.

Defibrillator 200 moreover includes a discharge circuit 255. When thedecision is to shock, processor 230 can be configured to controldischarge circuit 255 to discharge through the patient the electricalcharge stored in energy storage module 250. When so controlled, circuit255 can permit energy stored in module 250 to be discharged to nodes214, 218, and from there also to defibrillation electrodes 204, 208, soas to cause a shock to be delivered to the patient. Circuit 255 caninclude one or more switches 257. Switches 257 can be made in a numberof ways, such as by an H-bridge, and so on. In some embodiments,discharge circuit 255 is configurable to output multiphasic shocks, suchas for example, biphasic shocks. In some embodiments, energy storagemodule has multiple distinct energy submodules (e.g., capacitors) anddischarge circuit 255 is configurable to discharge a different energystorage submodule for each phase of a multiphasic shock. In someembodiments, circuit 255 can also be controlled via user interface 280.

Defibrillator 200 can optionally include a communication module 290, forestablishing one or more wired or wireless communication links withother devices of other entities, such as a remote assistance center,Emergency Medical Services (EMS), and so on. Module 290 may also includesuch sub-components as may be deemed necessary by a person skilled inthe art, for example an antenna, portions of a processor, supportingelectronics, outlet for a telephone or a network cable, etc. This way,data, commands, etc. can be communicated. The data can include patientdata, event information, therapy attempted, CPR performance, systemdata, environmental data, and so on. Defibrillator 200 in someembodiments can optionally include other components.

Returning to FIG. 1 , in embodiments, one or more of the components ofthe shown WCD system have been customized for patient 82. Thiscustomization may include a number of aspects. For instance, supportstructure 170 can be fitted to the body of patient 82. For anotherinstance, baseline physiological parameters of patient 82 can bemeasured, such as the heart rate of patient 82 while resting, whilewalking, motion detector outputs while walking, etc. Such baselinephysiological parameters can be used to customize the WCD system, inorder to make its diagnoses more accurate, since the patients' bodiesdiffer from one another. Of course, such parameters can be stored in amemory of the WCD system, and so on.

A programming interface can be made according to embodiments, whichreceives such measured baseline physiological parameters. Such aprogramming interface may input automatically in the WCD system thebaseline physiological parameters, along with other data.

FIG. 3 is a diagram showing sample components of an externaldefibrillator 301 similar to the external defibrillator 200 of FIG. 2 ,in which some components are shown in more detail, according toembodiments. External defibrillator 301 can be implemented in a WCD insome embodiments to deliver appropriate therapy (e.g., defibrillationshocks, cardioversion shocks, pacing, etc.) to a patient with anarrhythmia.

In this embodiment, external defibrillator 301 includes a measurementcircuit 320 and memory 338, both coupled to a processor 330. Externaldefibrillator 301 also includes other modules and components as shown inFIG. 2 , but are omitted in FIG. 3 as they have already been describedin detail in conjunction with FIG. 2 .

Memory 338, in some embodiments, is similar to memory 238 (FIG. 2 ) andin addition is configured with at least two algorithms for determiningthe duration of a shock as a function of TTI. In FIG. 3 , memory 338 isconfigured with three duration algorithms 341-343. In some embodiments,external defibrillator 301 is also configured so that no single shockcan exceed a set duration. While some practitioners may not consider afixed duration to be an “algorithm” in a technical sense, for purposesof this disclosure a maximum duration being used instead of a largerduration determined by another algorithm is a referred to herein as aMax Duration Waveform algorithm. In one embodiment, duration algorithms341-343 are the Walcott Algorithm, the CE Algorithm, and the MaxDuration algorithm, respectively. The Walcott Algorithm, CE Algorithmand the Max Duration Algorithms are described in more detail below.Further, in some embodiments, memory 338 is configured with at least twoalgorithms (not shown) for shaping the waveform of a shock to bedelivered to a patient with the duration determined using durationalgorithms such as described above. For example, the waveform algorithmcan be a biphasic truncated exponential (BTE) waveform with equalduration phases, a biphasic truncated exponential waveform with theduration of the second phase being ⅔ of the first phase, rectilinearbiphasic waveforms, biphasic square waveforms, pulsed waveforms, orwaveforms with three or more phases. In some embodiments, the durationalgorithm also defines the waveform such as, for example, the Walcottalgorithm which defines the duration of each phase of a BTE waveform. Ofcourse, other duration algorithms may also define the duration of eachphase. In some embodiments, the external defibrillator is alsoconfigured with a minimum duration for the shock such as, for example, 4ms.

In some embodiments, other algorithms can be used. For example, in someembodiments a modified version of the Walcott Algorithm can be used inwhich the shock duration is calculated in the same way as the originalWalcott Algorithm but the periods of the waveform are modified (e.g., tobe equal). Other algorithms include for example, monophasic truncatedexponential algorithms, or algorithms based on a fixed duration orstep-wise control of the duration for given range of TTI.

In addition, memory 338 can be configured with one or more voltagecompensation algorithms (not shown) for determining a charge voltage fora capacitor energy storage module used in external defibrillator 301 toprovide the energy for the shock. In some embodiments, the chargevoltage of a capacitor used in external defibrillator 301 has a maximumvoltage rating and known capacitance, which is accounted for in thevoltage compensation algorithm. As will be described further below, inembodiments with the voltage compensation algorithm, externaldefibrillator 301 can deliver shocks with the desired energy to patientswith higher TTIs than is typically delivered by external defibrillatorswith no voltage compensation.

In this embodiment, measurement circuit 320 is similar to measurementcircuit 220 (FIG. 2 ), and more specifically shows an impedancemeasurement circuit 305 coupled to sensors coupled to the patient whichare used in this embodiment to measure a patient's TTI. In someembodiments, impedance measurement circuit 305 provides a low voltageconstant current AC signal (e.g., a series of pulses) to the patient viathe sensors, such as described in U.S. Pat. No. 5,999,852 entitled“Defibrillator Method and Apparatus”, which is incorporated herein byreference in its entirety. Impedance measurement circuit 305 candetermine the TTI itself, or in other embodiments a TTI measurementmodule 336A of processor 330 determines the TTI.

Processor 330, in this embodiment, also includes a duration algorithmselection module 336B and a shock duration module 336C. Durationalgorithm selection module 336B is configured to select between theduration algorithms configured in memory 338 based on the patient'smeasured TTI. In some embodiments, duration algorithm selection module336B is configured to select between the duration algorithms 341-343 asa function of the measured patient TTI. For example, in someembodiments, one or more TTI thresholds are preset by an administrator,while in other embodiments the TTI thresholds are dynamically determinedby processor 330 as a function of the measured patient TTI or the chargevoltage in embodiments with voltage compensation and/or selectable shockenergies. Duration algorithm selection module 336B then compares themeasured TTI to the one or more thresholds. In some embodiments, if themeasured TTI is below a first threshold, module 336B is configured toselect Algorithm 1, and if the measured TTI is above the firstthreshold, module 336B is configured to select Algorithm 2. Inembodiments with a third duration algorithm, a second threshold (higherthan the first threshold) is determined or preset. If the measured TTIis above the second threshold, then module 336B is configured in thisembodiment to select Algorithm 3.

In some other embodiments, processor 330 is configured to select theduration algorithm dynamically by determining the energies delivered byeach of the algorithms and selecting the algorithm with the highestdelivered energy (or the energy closest to the selected energy in someother embodiments).

Using the algorithm selected by module 336B, shock duration module 336Cthen determines the duration of the shock to be delivered to thepatient, as a function of the measured TTI. In some embodiments, theshock is delivered in the form of a biphasic truncated exponential (BTE)waveform. In other embodiments, in addition to previously mentionedwaveforms, other waveforms are used such as, for example, rectilinearbiphasic waveforms, biphasic square waveforms, pulsed waveforms, orwaveforms with three or more phases.

In some embodiments, in addition to controlling the duration of theshock, the charge voltage of the energy storage module (e.g., energystorage module 252 in FIG. 2 ) is controlled by processor 330 (or byprocessor 230 FIG. 2 ) as a function of patient TTI. This is sometimesreferred to as voltage compensation. For example, in patients withrelatively high TTI, for a given charge voltage, the energy delivered tothe patient may not reach the desired level within the maximum duration.In these embodiments, the processor causes the energy storage module tobe charged to a higher charge voltage for patients with relatively highTTI. This in effect causes the values of the first and second thresholdsto increase (or move to the right in FIG. 4A, described below). As aresult, more patients are likely to receive shocks with at least the CEAlgorithm energy level. That is, this voltage compensation providesconstant energy for patients with greater TTI than is achievable byduration compensation along. In some embodiments, the voltagecompensation is performed in a step-wise manner based on the measuredpatient TTI. In other embodiments, the voltage compensation is performedin a continuous manner as a function of the measure patient TTI.

FIG. 4A shows a chart illustrating an example of the thresholds andduration algorithms, according to embodiments. FIG. 4A shows energy (J)as a function of patient TTI (ohms). Note, the values for energy and TTIare illustrative for an example external defibrillator, and could bedifferent for other defibrillators. In this example, for relatively lowTTI (i.e., below Threshold 1), the Walcott Algorithm is selected (e.g.,by duration selection module 336B in FIG. 3 ) to determine the shockduration. The durations of the Walcott algorithm result in shocks havingenergies that is inversely proportional to TTI. As can be seen in FIG.4A, this results in a relatively high energy shock for low TTI patientsranging from about 150 J to about 135 J.

For “moderate” TTI patients (e.g., patients having a TTI betweenThreshold 1 and Threshold 2), the CE Algorithm is selected in thisembodiment. As the name of the algorithm implies, such patients allreceive the same energy, which in this example is about 135 J. Thisenergy can be preset (for example, in a WCD or simple AEDs), orselectable by a user or rescuer (for example, via a user interface inexternal defibrillators designed for trained operators).

For “high” TTI patients (e.g., patients with TTI greater than Threshold2), the Max Duration algorithm is selected in this embodiment. In someembodiments, the maximum duration of the shock according to the MaxDuration Algorithm is preset in the external defibrillator by anadministrator, physician, or in the factory when the externaldefibrillator is manufactured. In some embodiments, the maximum durationof the shock is less than 25 ms. As shown in FIG. 4A, using the MaxDuration Algorithm, the energy delivered to the patient drops off as afunction of patient TTI, reflecting that the delivered energy for afixed duration decreases as TTI increases.

In addition to controlling total waveform duration, in embodiments usingmultiphasic shock waveforms, processor 330 also controls the relativeproportion of the entire duration dedicated to the phases. FIG. 4B showsthe phases of an example BTE waveform in terms of current (I) vs time(T). The duration of the first phase of the waveform is T₁, and with aninitial current of I₁ that decays exponentially based on the patient'sTTI and other resistances in the system such as from components in theexternal defibrillator and between the electrodes and the patient'sskin. The second phase of the BTE waveform has a duration of T₂, and atthe end of which the truncated waveform has a current of I₄.

In some embodiments, processor 330 is configured to control a singlephase of the BTE waveform (relative duration) to improve defibrillationefficacy. For example, as shown in FIG. 4B, the BTE waveform has a totalduration of d=T₁+T₂ where the relative duration of T₁ is d_(1rel)=T₁/d,and the relative duration of T₂ is d_(2rel)=T₂/d. In some embodiments,d_(1rel) is a value between 0.3 and 0.7 and is fixed regardless of TTI.In other embodiments, the relative duration of each phase varies as TTIvaries. In yet other embodiments d_(1rel) is fixed in a given range orranges of TTI while it varies in another range or ranges of TTI. Theserelative durations can be selected by an administrator, physician, etc.,or preset when the external defibrillator is manufactured. Theserelative durations can be used to define waveform algorithms aspreviously described.

Walcott Algorithm

In the Walcott Algorithm, the total duration of the shock, d, isdescribed by the equations below.

$\begin{matrix}{d = {T_{1} + {{0.67 \cdot T_{1}}{\forall{R_{pt} < x}}}}} & (1)\end{matrix}$ $\begin{matrix}{{{where}T_{1}} = {{{- \gamma} \cdot \ln}\left( \frac{\tau_{m}}{\tau_{s}} \right)}} & (2)\end{matrix}$

and τ_(s) and γ are described by equations 3 and 4.

$\begin{matrix}{\tau_{s} = {C_{d} \cdot \left( {R_{pt} + R_{d}} \right)}} & (3)\end{matrix}$ $\begin{matrix}{\gamma = \frac{\tau_{s} \cdot \tau_{m}}{\tau_{s} - \tau_{m}}} & (4)\end{matrix}$C_(d) is the device capacitance, R_(d) is the device impedance, R_(pt)is the patient TTI, τ_(m) is the Walcott Model time constant and isbetween 4 and 8 ms, and x is a first threshold. In one embodiment, thefirst threshold is determined by the intercept of the energy deliverycurves for the Walcott and CE Algorithms and the second threshold isdetermined by the TTI at which the device parameters (e.g., thecapacitance of the energy storage module, the charge voltage, deviceimpedances) can no longer deliver a shock with the energy set by the CEAlgorithm In some embodiments, the Walcott Algorithm is modified so thatthe total duration d is the same (as in the original Walcott Algorithm),but the durations of the phases are slightly different. In oneembodiment, the modified Walcott Algorithm has the phases being thesame, as opposed to the second phase being 0.67 of the first phase as inthe original Walcott Algorithm (see equation 1 above). In someembodiments, the modified Walcott Algorithm includes a minimum durationfor the shock such as, for example, 4 ms.

Constant Energy (CE) Algorithm

Given the device configuration (capacitance, resistance, chargevoltage), desired defibrillation energy, and measured patient impedancethe following equation is used to calculate the total duration of thedefibrillation waveform.

$\begin{matrix}{{T_{1} + T_{2}} = {{\frac{- \tau_{s}}{2} \cdot {\ln\left( {1 - \frac{E_{pt} \cdot \left( {R_{pt} + R_{d}} \right)}{0.5 \cdot R_{pt} \cdot V_{chg}^{2} \cdot C_{d}}} \right)}}{\forall{R_{pt} > x}}}} & (5)\end{matrix}$where T₁+T₂ is the total duration of the waveform and should not exceedapproximately 25 ms or be less than 4 ms, τ_(s) is the time constant forthe circuit consisting of the device and patient, R_(pt) is thepatient's measured TTI, R_(d) is the device impedance, E_(pt) is thetarget energy to be delivered to the patient, V_(chg) is the chargevoltage on the device capacitor, and C_(d) is the device capacitance. Insome embodiments, the CE algorithm is used only when R_(pt) is greaterthan x, where x is the first threshold.

In accordance with this disclosure, external defibrillators canadvantageously deliver effective shocks with greater energy to a widerrange of patients than with any one waveform compensation techniquealone, thereby maximizing the defibrillation efficacy. This disclosurecan be especially advantageous in a defibrillator of limited energystorage capacity, such as a WCD.

The various embodiments of the devices and/or systems disclosed in thisdocument perform functions, processes and/or methods as described above.These functions, processes and/or methods may be implemented by one ormore devices that include logic circuitry. Such a device can bealternately called a computer, and so on. It may be a standalone deviceor computer, such as a general-purpose computer, or part of a devicethat has one or more additional functions. In some embodiments, thecomputer is a specialized computer adapted to and optimally configuredfor a specific purpose such as for example, providing therapy shocks inemergency situations. The logic circuitry may include a processor andnon-transitory computer-readable storage media, such as memories, of thetype described in this document. Often, for the sake of convenience, itis preferred to implement and describe a program as variousinterconnected distinct software modules or features. These, along withdata are individually and also collectively referred to herein assoftware. In some instances, software is combined with hardware, in amix called firmware.

Various embodiments of methods and algorithms are described below. Thesemethods and algorithms are not necessarily inherently associated withany particular logic device or other apparatus. Rather, they can beadvantageously implemented by programs for use by a computing machine,such as a general-purpose computer, a special purpose computer, amicroprocessor, a microcontroller, a processor and/or a combination ofthese devices such as described elsewhere in this document, and so on.

This detailed description includes flowcharts, display images,algorithms, and symbolic representations of program operations within atleast one computer readable medium. An economy is achieved in that asingle set of flowcharts is used to describe both programs, and alsomethods. So, while flowcharts describe methods in terms of boxes, theyalso concurrently describe programs.

FIG. 5 is a flow diagram illustrating a method 500 for determining shockduration, according to embodiments. In an operation 505, a firstthreshold is stored. In some embodiments, the first threshold is storedin a memory of an external defibrillator such as for example, memory 238(FIG. 2 ) or memory 338 (FIG. 3 ).

In an operation 507 and an operation 509, first and second algorithmsfor determining a duration of a shock are stored, respectively. In someembodiments, the algorithms are stored in a memory of an externaldefibrillator such as for example, memory 238 (FIG. 2 ) or memory 338(FIG. 3 ). In some embodiments, the first algorithm is the WalcottAlgorithm. In other embodiments, the first algorithm is a modifiedWalcott Algorithm. In some embodiments, the second algorithm is the CEAlgorithm. In yet other embodiments, other duration algorithms or othermodifications of the Walcott or CE Algorithms can be used for the firstand second algorithms such as, for example, the previously mentionedconstant duration, step-wise duration, and monophasic truncatedexponential algorithms.

In an operation 511, the patient's TTI is measured. In some embodiments,the patient's TTI is measured via external sensors such as ECG ortherapy electrodes (e.g., electrodes 204, 208, 209 in FIG. 2 ) by ameasurement circuit of an external defibrillator such as, for example,measurement circuit 220 (FIG. 2 ) or impedance measurement circuit 305in conjunction with TTI measurement module 336A (FIG. 3 ).

The duration of the shock is then determined based on the measuredpatient TTI. In some embodiments, the duration is determined by aprocessor of an external defibrillator such as, for example, processor230 (FIG. 2 ) or processor 330 (FIG. 3 ). Embodiments of this processare described in more detail below.

In embodiments, in an operation 513, the measured TTI is analyzed orcompared to determine if it is greater than the first threshold. In someembodiments, this determination is performed by a processor such as, forexample, duration selection module 336B (FIG. 3 ) of processor 330.

If the measured TTI is not greater than (or not greater than or equal toin some embodiments) the first threshold, in an operation 515 the shockduration is determined using the first algorithm. In some embodiments,the first algorithm (per operation 507) is performed by a shock durationmodule such as, for example, shock duration module 336C of processor 330(FIG. 3 ).

If the measured TTI is greater than (or greater than or equal to in someembodiments) the first threshold, in an operation 517 the shock durationis determined using the second algorithm. In some embodiments, thesecond algorithm (per operation 509) is performed by a shock durationmodule such as, for example, shock duration module 336C of processor 330(FIG. 3 ).

In an operation 521, the external defibrillator is caused to output ashock with the duration determined in operation 515 or 517, depending onthe measured patient TTI. In some embodiments, this operation isperformed by a processor of an external defibrillator such as, forexample, processor 230 (FIG. 2 ) or processor 330 (FIG. 3 ), controllingother components of the external defibrillator (e.g., as described abovein conjunction with FIGS. 2 and 3 ).

FIG. 6 is a flow diagram illustrating a method 600 for determining shockduration, according to embodiments. In an operation 601, a firstthreshold and a second threshold are stored. In some embodiments, thefirst and second thresholds are stored in a memory of an externaldefibrillator such as for example, memory 238 (FIG. 2 ) or memory 338(FIG. 3 ).

In an operation 602, first and second algorithms for determining aduration of a shock are stored. In some embodiments, the algorithms arestored in a memory of an external defibrillator such as for example,memory 238 (FIG. 2 ) or memory 338 (FIG. 3 ). In some embodiments, thefirst algorithm is the Walcott Algorithm. In other embodiments, thefirst algorithm is a modified Walcott Algorithm. In some embodiments,the second algorithm is the CE Algorithm. In yet other embodiments,other duration algorithms or other modifications of the Walcott or CEAlgorithms can be used for the first and second algorithms such as, forexample, the previously mentioned constant duration, step-wise duration,and monophasic truncated exponential algorithms.

In an operation 603, a third algorithm for determining a duration of ashock is stored. In some embodiments, the algorithm is stored in thesame memory as described above in conjunction with operation 602. Insome embodiments, the third algorithm is the previously described MaxDuration Algorithm. In other embodiments, other duration algorithms ormodifications of the Walcott or CE or Max Duration Algorithms are usedfor the third algorithm.

In an operation 611, the patient's TTI is measured. In some embodiments,the patient's TTI is measured via external sensors such as ECG ortherapy electrodes (e.g., electrodes 204, 208, 209 in FIG. 2 ) by ameasurement circuit of an external defibrillator such as, for example,measurement circuit 220 (FIG. 2 ) or impedance measurement circuit 305in conjunction with TTI measurement module 336A (FIG. 3 ).

The duration of the shock is then determined based on the measuredpatient TTI, in embodiments. In some embodiments, the duration isdetermined by a processor of an external defibrillator such as, forexample, processor 230 (FIG. 2 ) or processor 330 (FIG. 3 ). Embodimentsof this process are described in more detail below.

In embodiments, in an operation 613, the measured TTI is analyzed orcompared to determine if it is greater than the first threshold. In someembodiments, this determination is performed by a processor such as, forexample, duration selection module 336B (FIG. 3 ) of processor 330.

If the measured TTI is not greater than (or not greater than or equal toin some embodiments) the first threshold, in an operation 615 the shockduration is determined using the first algorithm. In some embodiments,the first algorithm (per operation 602) is performed by a shock durationmodule such as, for example, shock duration module 336C of processor 330(FIG. 3 ).

If the measured TTI is greater than (or greater than or equal to in someembodiments) the first threshold, in an operation 616 the measured TTIis analyzed or compared to determine if it is greater than the secondthreshold. In some embodiments, this determination is performed by theprocessor as described above in conjunction with operation 613.

If the measured TTI is not greater than (or not greater than or equal toin some embodiments) the second threshold, in an operation 617 the shockduration is determined using the second algorithm. In some embodiments,the second algorithm (per operation 602) is performed by a shockduration module such as, for example, shock duration module 336C ofprocessor 330 (FIG. 3 ).

If the measured TTI is greater than (or greater than or equal to in someembodiments) the second threshold, in an operation 619 the shockduration is determined using the third algorithm. In some embodiments,the third algorithm (per operation 603) is performed by a shock durationmodule such as, for example, shock duration module 336C of processor 330(FIG. 3 ).

In an operation 621, the external defibrillator is caused to output ashock with the duration determined in operation 615 or 617 or 619,depending on the measured patient TTI. In some embodiments, thisoperation is performed by a processor of an external defibrillator suchas, for example, processor 230 (FIG. 2 ) or processor 330 (FIG. 3 ),controlling other components of the external defibrillator (e.g., asdescribed above in conjunction with FIGS. 2 and 3 ).

FIG. 7 is a flow diagram illustrating a method 700 for determiningcharge voltage and shock duration, according to embodiments. In anoperation 703, first, second and third algorithms for determining aduration of a shock are stored. In some embodiments, the algorithms arestored in a memory of an external defibrillator such as for example,memory 238 (FIG. 2 ) or memory 338 (FIG. 3 ). In some embodiments, thefirst algorithm is the Walcott Algorithm. In other embodiments, thefirst algorithm is a modified Walcott Algorithm. In some embodiments,the second algorithm is the CE Algorithm. In some embodiments, the thirdalgorithm is the Max Duration Algorithm In yet other embodiments, otherduration algorithms or other modifications of the Walcott or CE or MaxDuration Algorithms can be used for the first, second and thirdalgorithms such as, for example, the previously mentioned constantduration, step-wise duration, and monophasic truncated exponentialalgorithms.

In an operation 705, the patient's TTI is measured. In some embodiments,the patient's TTI is measured via external sensors such as ECG ortherapy electrodes (e.g., electrodes 204, 208, 209 in FIG. 2 ) by ameasurement circuit of an external defibrillator such as, for example,measurement circuit 220 (FIG. 2 ) or impedance measurement circuit 305in conjunction with TTI measurement module 336A (FIG. 3 ).

In an operation 707, a charge voltage is determined based on themeasured patient TTI. In some embodiments, the charge voltage isdetermined by a processor of an external defibrillator such as, forexample, processor 230 (FIG. 2 ) or processor 330 (FIG. 3 ) using avoltage compensation algorithm. In some embodiments, the voltagecompensation algorithm increases the charge voltage of an energy storagemodule such as, for example, energy storage module 250 (FIG. 2 ), andthe processor then causes an energy storage module of the externaldefibrillator to be charged to the determined voltage. In someembodiments, the voltage compensation algorithm increases the chargevoltage as a step-wise function of measured patient TTI, and in otherembodiments as a continuous function of measured patient TTI.

In an operation 709, a first threshold and a second threshold aredetermined. In some embodiments, the first and second thresholds aredetermined by a processor such as described above in conjunction withoperation 707 as a function of the charge voltage and/or measuredpatient TTI. In some embodiments, the determined first and secondthreshold are then stored in a memory of an external defibrillator suchas for example, memory 238 (FIG. 2 ) or memory 338 (FIG. 3 ).

The duration of the shock is then determined based on the measuredpatient TTI, in embodiments. In some embodiments, the duration isdetermined by a processor of an external defibrillator such as, forexample, processor 230 (FIG. 2 ) or processor 330 (FIG. 3 ). Embodimentsof this process are described in more detail below.

In embodiments, in an operation 713, the measured TTI is analyzed orcompared to determine if it is greater than the first threshold. In someembodiments, this determination is performed by a processor such as, forexample, duration selection module 336B (FIG. 3 ) of processor 330.

If the measured TTI is not greater than (or not greater than or equal toin some embodiments) the first threshold, in an operation 715 the shockduration is determined using the first algorithm. In some embodiments,the first algorithm (per operation 703) is performed by a shock durationmodule such as, for example, shock duration module 336C of processor 330(FIG. 3 ).

If the measured TTI is greater than (or greater than or equal to in someembodiments) the first threshold, in an operation 716 the measured TTIis analyzed or compared to determine if it is greater than the secondthreshold. In some embodiments, this determination is performed by theprocessor as described above in conjunction with operation 713.

If the measured TTI is not greater than (or not greater than or equal toin some embodiments) the second threshold, in an operation 717 the shockduration is determined using the second algorithm. In some embodiments,the second algorithm (per operation 703) is performed by a shockduration module such as, for example, shock duration module 336C ofprocessor 330 (FIG. 3 ).

If the measured TTI is greater than (or greater than or equal to in someembodiments) the second threshold, in an operation 719 the shockduration is determined using the third algorithm. In some embodiments,the third algorithm (per operation 703) is performed by a shock durationmodule such as, for example, shock duration module 336C of processor 330(FIG. 3 ).

In an operation 721, the external defibrillator is caused to output ashock with the duration determined in operation 715 or 717 or 719,depending on the measured patient TTI. In some embodiments, thisoperation is performed by a processor of an external defibrillator suchas, for example, processor 230 (FIG. 2 ) or processor 330 (FIG. 3 ),controlling other components of the external defibrillator (e.g., asdescribed above in conjunction with FIGS. 2 and 3 ).

Time to Ratio (UR) Embodiments

FIG. 8 is a diagram showing sample components of an externaldefibrillator 801 similar to external defibrillator 200 (FIG. 2 ) andexternal defibrillator 301 (FIG. 3 ), in which some components are shownin more detail, according to embodiments. External defibrillator 801 canbe implemented in a WCD in some embodiments to deliver appropriatetherapy (e.g., defibrillation shocks, cardioversion shocks, pacing,etc.) to a patient with an arrhythmia.

In this embodiment, external defibrillator 801 includes measurementcircuit 320, memory 338, and processor 330 as described above inconjunction with FIG. 3 , and other modules and components as shown inFIG. 2 (but omitted in FIG. 8 as they have already been described indetail in conjunction with FIG. 2 ).

Memory 338 of external defibrillator 801, in some embodiments, issimilar to memory 338 (FIG. 3 ), being configured with at least twoduration algorithms such as for example, the Walcott Algorithm, theMod-cott Algorithm, the CE Algorithm or the previously described MaxDuration Algorithm. In some embodiments, the duration algorithms includea minimum duration (e.g., 4 ms) for the shock. In addition, in someembodiments memory 338 is configured with at least one algorithm (notshown) for shaping (e.g., determining the durations of each phase of amultiphasic waveform) the waveform of a shock to be delivered to apatient. In some embodiments, the waveform is a BTE waveform with equalphases. In other embodiments, the waveform is a multiphasic waveformwith one phase being an exponential, and another phase being arectilinear. In some embodiments, the phase durations of a multiphasicexponential waveform are configured in a similar manner as describedabove in conjunction with FIG. 4B. In some embodiments, one or more ofthe duration algorithms also define the waveform (e.g., the duration ofeach phase of a BTE waveform as defined by the Walcott or equal phaseMod-cott duration algorithms).

In this embodiment, measurement circuit 320 is similar to measurementcircuit 320 (FIG. 3 ), and more specifically also shows a voltagemeasurement circuit 805 coupled to the energy storage module such as,for example, energy storage module 250 (FIG. 2 ). In some embodiments,voltage measurement circuit 505 measures the charge voltage of acapacitor of the energy storage module while a shock is beingadministered to the patient.

Processor 330 of external defibrillator 801, in some embodiments, issimilar to processor 330 (FIG. 3 ) and in addition includes a Time ToRatio (TTR) module 836. In some embodiments, TTR module 836 isconfigured to determine the time it takes a fully charged energy storagemodule to discharge to a selected voltage ratio (also referred to as thedecay time). For example, in some embodiments, the ratio is 82% of thepeak voltage. The decay time needed to discharge to the set voltageratio can then be used to calculate the durations according to the firstand second duration algorithms 342 and 342 as described below.

In general, the decay time τ₁ for a ratio of 82% can be calculatedaccording to equation (6) below.τ₁ =C _(d)·(R _(pt) +R _(d))·ln(0.82)  (6)where the capacitance and resistances are defined as in equation (3)above. In this embodiment, the patient TTI is not measured and insteadTTR module 836 measures τ₁ during delivery of the shock. But as can beseen in equation (6), patients with a relatively low TTI will have alower decay time τ₁ than patients with a relatively high TTI.

In one embodiment, duration algorithm 341 of FIG. 8 is configured todetermine the duration D_(MC) of a Mod-Cott (modified Walcott) waveformusing the measured τ₁ according to equation (7) below. In oneembodiment, the Mod-Cott waveform is the same as the Walcott waveformexcept that it has phases of equal duration.

$\begin{matrix}{D_{MC} = {\frac{5}{3}\left( {\left( {\left( {\left( \frac{- \tau_{1}}{\ln(0.82)} \right) \cdot \tau_{m}} \right) \div \left( {\left( \frac{- \tau_{1}}{\ln(0.82)} \right) - \tau_{m}} \right)} \right) \cdot {\ln\left( \frac{\tau_{m}}{\frac{- \tau_{1}}{\ln(0.82)}} \right)}} \right)}} & (7)\end{matrix}$

where τ_(m) is the Walcott Model time constant and in in this embodimentis 0.0051. In other embodiments, other duration algorithms based on TTIcan be mathematically recast as a function the decay time τ₁ instead ofTTI by one skilled in the art after review of this disclosure.

In some embodiments, duration algorithm 342 of FIG. 8 is configured todetermine the duration D_(CE) of a CE algorithm waveform as a functionof the measured decay time τ₁ instead of measured patient TTI. In someembodiments, equation (5) above is solved to be a function of a UR of82%. For this UR, it can be shown that for a nominal 150 J ConstantEnergy waveform sourced from a 138 μF capacitor charged to 1600 volts,the duration D_(CE) can be determined as a function of the measured τ₁according to equation (8) below.D _(CE)=6.13·τ₁  (8)In other embodiments, different shock energies, capacitances, and/orcharge voltage will result in the measured decay time τ₁ beingmultiplied by a different constant.

In some embodiments, the capacitance of a nominally 138 μF energystorage module is calibrated. In such embodiments, the duration D_(CE)can be determined as a function of the measured τ₁ according to equation(9) below.

$\begin{matrix}{D_{CE} = {\left( {6.13 \cdot \tau_{1}} \right)/\left( \frac{Ccal}{138µF} \right)}} & (9)\end{matrix}$where Ccal is the actual capacitance measured during calibration.

In some embodiments, processor 330 of FIG. 8 then compares the durationsdetermined using the first and second duration algorithms, and selectsthe algorithm having the larger duration. In one embodiment, TTR module836 performs this selection. Using the selected algorithm, processor 330of FIG. 8 , then controls the discharge circuit (e.g., discharge circuit255 of FIG. 2 ) so that the shock delivered to the patient has thewaveform associated with the selected duration algorithm. In someembodiments where the first duration algorithm is the Walcott algorithmand the second waveform algorithm is the CE duration algorithm, theselection of the duration algorithm somewhat follows the graph of FIG.4A in that relatively low decay times will result in selection of theWalcott algorithm and a moderate decay time will result in the selectionof the CE algorithm. In some embodiments, both duration algorithms areassociated with a BTE waveform having equal duration phases. In otherembodiments, the duration algorithm may each be associated with awaveform algorithm with different phase durations, different types ofwaveforms (e.g., exponential versus rectilinear), different number ofphases, or even with specific phases having shapes according todifferent types of waveforms (e.g., first phase being rectilinear and asecond phase being exponential).

FIG. 9 is a flow diagram illustrating a method 900 for selecting a shockduration based on TTR, according to embodiments. In an operation 905, afirst waveform algorithm and a first duration algorithm are stored. Insome embodiments a single algorithm may define both a duration andwaveform (e.g., the Walcott Algorithm). In some embodiments, the firstwaveform algorithm is for delivering a shock having Walcott waveform(i.e., a BTE waveform with the second phase having a duration that is ⅔of the first phase) and first duration algorithm is for determining theduration the Walcott waveform as a function of measured decay time(i.e., the Walcott Algorithm as a function of TTR). In some otherembodiments, the Mod-cott waveform algorithm is used instead of theWalcott waveform algorithm. In some embodiments, these waveforms arestored in a memory of an external defibrillator such as for example,memory 338 (FIG. 8 ).

In an operation 907, a second waveform algorithm and a second durationalgorithm are stored. In some embodiments, the second waveform algorithmis for delivering a shock having an equal phase duration BTE waveformand second duration algorithm is for determining the duration the CEwaveform as a function of measured decay time (i.e., the CE Algorithm asa function of TTR). In some embodiments, if the determined durationexceeds a predetermined or selected maximum, the duration is then set tothis maximum. In some embodiments, these waveform algorithms are storedin a memory of an external defibrillator such as for example, memory 338(FIG. 8 ). As stated earlier in operation 905, the waveform algorithmmay be the same as the duration algorithm (e.g., the Mod-cott Algorithmcan define both the total duration and the duration of each phase of aBTE waveform). In some embodiments, while durations algorithms 1 and 2are different, the waveform algorithms may be the same (e.g., a BTEwaveform with equal phases). In yet other embodiments, other waveformand duration algorithms or other modifications of the Walcott or CEAlgorithms can be used for the first and second waveform and durationalgorithms such as, for example, monophasic truncated exponentialalgorithms.

In an operation 909, a delivery of a shock to the patient is initiatedand the decay to reach a selected or set ratio measured. In someembodiments, the ratio is 82%. In other embodiments, the ratio can bedifferent within the range from about 80% to about 99%, and so thatthere is still time to control the shock to have a waveform according toboth first and second waveform algorithms. For example, if the ratio istoo low (meaning more time is needed to discharge to that lowerpercentage) it might be that the discharge is past the time for endingthe first phase of one of the waveform algorithms, especially asdescribed below, some additional time may be needed to determinedurations using both the first and second algorithms. If the ratio istoo high, the decay time measurement might be less accurate. In someembodiments, this operation is performed by a processor of an externaldefibrillator such as, for example, TTR module 836 of processor 330(FIG. 8 ), controlling and/or receiving measurements from othercomponents of the external defibrillator (e.g., as described above inconjunction with FIGS. 2, 3 and 8 ).

In an operation 911, the first and second duration algorithms areexecuted to determine durations of the waveforms according to the firstand second waveform algorithms. In some embodiments, shock durationmodule 336C of processor 330 (FIG. 8 ) determines these durations.

In embodiments, in an operation 913, the determined durations areanalyzed or compared, including comparing to a maximum duration in someembodiments For example, the maximum duration is set to a value below 25ms (e.g., 22 ms) in one embodiment. In some embodiments, the determineddurations are also compared to a minimum duration (e.g., 4 ms). In someembodiments, these determinations are performed by a processor such as,for example, processor 330 (FIG. 8 ). In some embodiments, thisdetermination is in particular performed by TTR module 836 and/orduration selection module 336B of processor 330 (FIG. 8 ).

If the determined duration of the waveform according to waveformalgorithm 1 (i.e., duration D1) is greater than (or greater than orequal to in some embodiments) the determined duration of the waveformaccording to waveform algorithm 2 (i.e. duration D2), in an operation915 the external defibrillator is controlled to deliver energy accordingto waveform algorithm 1 with duration D1. In some embodiments, waveformalgorithm 1 produces a BTE waveform with each phase having the sameduration. In some embodiments, this operation is performed by aprocessor of the external defibrillator such as, for example, processor330 (FIG. 8 ), controlling other components of the externaldefibrillator (e.g., as described above in conjunction with FIGS. 2, 3and 8 ).

In other embodiments configured with a selected or predetermined minimumduration, if in addition duration D1 is greater than the minimumduration, then operation 915 is performed as described above. However,if the determined duration is less than the minimum duration, then thealgorithm sets the duration to this minimum duration and causes theexternal defibrillator to deliver a shock to the patient according towaveform algorithm 1 having the minimum duration. In other embodimentsthe minimum duration waveform is another waveform different from thatproduced by waveform algorithm 1.

However, if duration D1 is not greater than (or not greater than orequal to in some embodiments) duration D2, in an operation 917 theexternal defibrillator is controlled to deliver energy according towaveform algorithm 2 with duration D2. In some embodiments, waveformalgorithm 2 also produces a BTE waveform with each phase having the sameduration. In other embodiments, waveform algorithm 2 produces adifferent waveform than waveform algorithm 1. In embodiments configuredwith a maximum duration, if in addition duration D2 is less than themaximum duration, operation 917 is performed as previously described. Insome embodiments, this determination is performed by the processor asdescribed above in conjunction with operation 915.

In embodiments configured with a maximum duration, responsive to bothdurations D1 and D2 exceeding the maximum duration, in an operation 919the external defibrillator is controlled to deliver energy with themaximum duration (e.g., the previously described Max DurationAlgorithm). In some embodiments, the waveform is a BTE waveform withequal duration phases. In some embodiments, the waveform algorithms 1-3are all the same in that they cause the shock to have a BTE waveformwith equal duration phases. In the methods described above, eachoperation can be performed as an affirmative step of doing, or causingto happen, what is written that can take place. Such doing or causing tohappen can be by the whole system or device, or just one or morecomponents of it. After review of this disclosure, a person of skill inthe art will recognize that the methods and the operations may beimplemented in many ways, including using systems, devices andimplementations described above. In addition, the order of operations isnot constrained to what is shown, and different orders may be possibleaccording to different embodiments. Examples of such alternate orderingsmay include overlapping, interleaved, interrupted, reordered,incremental, preparatory, supplemental, simultaneous, reverse, or othervariant orderings, unless context dictates otherwise. Moreover, incertain embodiments, new operations may be added, or individualoperations may be modified or deleted. The added operations can be, forexample, from what is mentioned while primarily describing a differentsystem, apparatus, device or method.

A person skilled in the art will be able to practice the presentinvention in view of this description, which is to be taken as a whole.Details have been included to provide a thorough understanding. In otherinstances, well-known aspects have not been described, in order to notobscure unnecessarily this description. Plus, any reference to any priorart in this description is not, and should not be taken as, anacknowledgement or any form of suggestion that such prior art formsparts of the common general knowledge in any country or any art.

This description includes one or more examples, but this fact does notlimit how the invention may be practiced. Indeed, examples, instances,versions or embodiments of the invention may be practiced according towhat is described, or yet differently, and also in conjunction withother present or future technologies. Other such embodiments includecombinations and sub-combinations of features described herein,including for example, embodiments that are equivalent to the following:providing or applying a feature in a different order than in a describedembodiment; extracting an individual feature from one embodiment andinserting such feature into another embodiment; removing one or morefeatures from an embodiment; or both removing a feature from anembodiment and adding a feature extracted from another embodiment, whileproviding the features incorporated in such combinations andsub-combinations.

In general, the present disclosure reflects preferred embodiments of theinvention. The attentive reader will note, however, that some aspects ofthe disclosed embodiments extend beyond the scope of the claims. To therespect that the disclosed embodiments indeed extend beyond the scope ofthe claims, the disclosed embodiments are to be considered supplementarybackground information and do not constitute definitions of the claimedinvention.

In this document, depending on the context, the phrases “constructed to”and/or “configured to” denote one or more actual states of constructionand/or configuration that is fundamentally tied to physicalcharacteristics of the element or feature preceding these phrases and,as such, reach well beyond merely describing an intended use. Any suchelements or features can be implemented in many ways, by a personskilled in the art after reviewing the present disclosure, beyond anyexamples shown in this document.

All parent, grandparent, great-grandparent, etc. patent applications,whether mentioned in this document or in an Application Data Sheet(“ADS”) of this patent application, are hereby incorporated by referenceherein as originally disclosed, including any priority claims made inthose applications and any material incorporated by reference, to theextent such subject matter is not inconsistent herewith.

In this description, a single reference numeral may be used consistentlyto denote a single item, aspect, component, or process. Moreover, afurther effort may have been made in the drafting of this description touse similar though not identical reference numerals to denote otherversions or embodiments of an item, aspect, component or process thatare identical or at least similar or related. Where made, such a furthereffort was not required, but was nevertheless made gratuitously toaccelerate comprehension by the reader. Even where made in thisdocument, such a further effort might not have been made completelyconsistently for all of the versions or embodiments that are madepossible by this description. Accordingly, the description controls indefining an item, aspect, component or process, rather than itsreference numeral. Any similarity in reference numerals may be used toinfer a similarity in the text, but not to confuse aspects where thetext or other context indicates otherwise.

This disclosure is meant to be illustrative and not limiting on thescope of the following claims. The claims of this document definecertain combinations and subcombinations of elements, features and stepsor operations, which are regarded as novel and non-obvious. Additionalclaims for other such combinations and subcombinations may be presentedin this or a related document. These claims are intended to encompasswithin their scope all changes and modifications that are within thetrue spirit and scope of the subject matter described herein. The termsused herein, including in the claims, are generally intended as “open”terms. For example, the term “including” should be interpreted as“including but not limited to,” the term “having” should be interpretedas “having at least,” etc. If a specific number is ascribed to a claimrecitation, this number is a minimum but not a maximum unless statedotherwise. For example, where a claim recites “a” component or “an”item, it means that it can have one or more of this component or item.

What is claimed is:
 1. An external defibrillator, comprising: two ormore electrodes configured to contact a patient; an energy storagemodule; a discharge circuit coupled with the energy storage module andat least two of the two or more electrodes; an impedance measuringcircuit; and one or more processors coupled to control the impedancemeasuring circuit and the discharge circuit, wherein the one or moreprocessors are configured to: measure a transthoracic impedance (TTI) ofthe patient using the impedance measuring circuit; and cause thedischarge circuit to apply a shock having a first phase duration and asecond phase duration to the patient using the at least two of the twoor more electrodes, wherein: when the TTI is below a predetermined TTIvalue, a first algorithm is used to determine the first and second phasedurations, wherein the first phase duration is equal to the second phaseduration; and when the TTI is not below the predetermined TTI value, asecond algorithm is used to determine the first and second phasedurations, wherein the first phase duration is not equal to the secondphase duration.
 2. The external defibrillator of claim 1, wherein thefirst algorithm or the second algorithm is based on a Walcott algorithm.3. The external defibrillator of claim 1, wherein the first algorithm orthe second algorithm is based on a constant energy (CE) algorithm. 4.The external defibrillator of claim 1, wherein the first algorithm orthe second algorithm is based on a maximum duration algorithm.
 5. Theexternal defibrillator of claim 1, wherein first algorithm or the secondalgorithm is based on a modified Walcott algorithm.
 6. The externaldefibrillator of claim 1, wherein the shock comprises a biphasictruncated exponential (BTE) waveform.
 7. A method for an externaldefibrillator comprising two or more electrodes configured to beattached to a patient, an energy storage module, a discharge circuitcoupled with the energy storage module and at least two of the two ormore electrodes and configured to output energy from the energy storagemodule to the patient in a form of a shock, wherein the shock has afirst phase duration and a second phase duration, an impedance measuringcircuit to measure a transthoracic impedance (TTI) of the patient usingat least some of the two or more electrodes, a memory to store a firstshock algorithm and a second shock algorithm, and one or more processorscoupled with the memory to control the impedance measuring circuit andthe discharge circuit, the method comprising: measuring the TTI of thepatient; causing the discharge circuit to apply the shock to the patientusing the first shock algorithm when the TTI is below a predeterminedTTI value, wherein the first phase duration is equal to the second phaseduration; and causing the discharge circuit to apply the shock to thepatient using the second shock algorithm when the TTI is below thepredetermined TTI value, wherein the first phase duration is not equalto the second phase duration.
 8. The method of claim 7, wherein thefirst shock algorithm or the second shock algorithm is based on aWalcott algorithm.
 9. The method of claim 7, wherein first shockalgorithm or the second shock algorithm is based on a modified Walcottalgorithm.
 10. The method of claim 7, wherein the first shock algorithmor the second shock algorithm is based on a constant energy (CE)algorithm.
 11. The method of claim 7, wherein the first shock algorithmor the second shock algorithm is based on a maximum duration algorithm.12. The method of claim 7, wherein the shock comprises a biphasictruncated exponential (BTE) waveform.
 13. The method of claim 7, whereinthe external defibrillator comprises a wearable cardioverterdefibrillator (WCD).
 14. A wearable cardioverter defibrillator (WCD),comprising: a support structure to be worn by a patient; two or moreelectrodes coupled with the support structure and configured to contactthe patient when the patient is wearing the support structure; an energystorage module; a discharge circuit, coupled with the energy storagemodule and two or more defibrillation electrodes, wherein the dischargecircuit is configured to output energy from the energy storage module;an impedance measuring circuit; and one or more processors, coupled withthe impedance measuring circuit and the discharge circuit, wherein theone or more processors are configured to: measure a transthoracicimpedance (TTI) of the patient using the impedance measuring circuit;and cause the discharge circuit to apply a shock having a first phaseduration and a second phase duration to the patient using the two of thetwo or more electrodes, wherein: when the TTI is below a predeterminedTTI value, a first algorithm is used to determine the first and secondphase durations, wherein the first phase duration is equal to the secondphase duration; and when the TTI is not below the predetermined TTIvalue, a second algorithm is used to determine the first and secondphase durations, wherein the first phase duration is not equal to thesecond phase duration.
 15. The WCD of claim 14, wherein the firstalgorithm or the second algorithm is based on a Walcott algorithm. 16.The WCD of claim 14, wherein first algorithm or the second algorithm isbased on a modified Walcott algorithm.
 17. The WCD of claim 14, whereinthe first algorithm or the second algorithm is based on a constantenergy (CE) algorithm.
 18. The WCD of claim 14, wherein the firstalgorithm or the second algorithm is based on a maximum durationalgorithm.
 19. The WCD of claim 14, wherein the shock comprises abiphasic truncated exponential (BTE) waveform.
 20. An externaldefibrillator, comprising: two or more electrodes configured to contacta patient; an energy storage module; a discharge circuit, coupled to theenergy storage module and at least two of the two or more electrodes; animpedance measurement module configured to measure a transthoracicimpedance (TTI) of the patient; and one or more processors coupled tothe discharge circuit and the impedance measurement module, the one ormore processors configured to: determine a shock duration, whereinresponsive to a measured TTI being smaller than a threshold, the one ormore processors are configured to determine the shock duration using afirst algorithm, and responsive to the measured TTI not being smallerthan the threshold, the one or more processors are configured todetermine the shock duration using a second algorithm that is differentfrom the first algorithm, and cause the discharge circuit to outputenergy from the energy storage module to the patient in a form of ashock having the determined shock duration using at least two of the twoor more electrodes.